The present invention refers to method for estimating the duration of the interruptions in the supply from the electric mains in an electric apparatus having an electronic control, in particular a household appliance, and to an apparatus implementing such a method.
It is known that certain electric apparatus, in particular household appliances, having a control system of the electronic type, include the clock function, usually available on a control panel.
With reference, in particular, to the field of household appliances of the so-called white type, such a clock function is typically associated with cooking apparatuses (ovens and cookers) and with apparatuses for household heating (boilers), while it is now also gradually extending to refrigerators, washing machines, dishwashers and water heaters.
It is also known that the availability of a clock function associated to the control system of a household appliance ensures several advantageous functions, such as:
the possibility of programming the execution in time of certain operating cycles of the household appliance, even if the user is not present (let us think for instance of an oven wherein a cooking program may be postponed, or about postponing a washing cycle for a dishwasher or washing machine);
the possibility of managing the opportunities offered by possible time based electricity rates, i.e. the possibility of programming the appliance operation at a time during the day when the electricity costs are lower than during other day times;
the possibility of supplying the user with current time information, which is not essential but useful, anyway.
However, it is obvious that such advantages become void if the above clock function is not protected against a possible interruption of the electric energy, or blackout, as it may usually happen for household appliances.
It is also known that the implementation of the cited clock function through a microcontroller is a simple and low-cost thing, since the operation itself of such an electronic device is beaten out by the frequency of a quartz or other oscillating element capable of generating a time base.
However, keeping a clock function activated during a blackout is quite a difficult operation, as it presumes the presence of an auxiliary source of electric current, such as a battery; now, a battery represents not only an expensive item, but also requires regular maintenance (battery replacement) by the user.
The fact that a clock function in white household appliances is typically not protected against possible mains supply interruptions represents undoubtedly a problem, which is the more serious the more blackouts are frequent.
For instance, in the case of present electric ovens equipped with a clock-programmer, where cooking is programmed to start at a certain time, a blackout of the mains supply, even a short one, while the user is not present, will normally cause cancellation of the programmed cooking and a consequent considerable nuisance for the user, who back home will find out that the oven did not perform the programmed function. Only highly expensive types of ovens provide for a sort of protection against blackouts, but this is typically limited to a few seconds only. In such an instance, a solution to the problem is to keep the microcontroller performing the clock function alive for a short time, using the energy stored within a high capacity electric capacitor; this is now possible thanks to the development of the CMOS electronic technology, through which consumption for electronic devices have been enormously reduced.
However, such a simple and fine solution has the drawback, anyway, of being unable to fully solve the problem, since it will only cover a limited time and have an expensive cost.
The problem might be solved, theoretically, in a complete way by using a buffer battery, to keep the clock function always activated also when no mains voltage is available. In this case, however, beside the direct cost of such a solution, further costs should be added to, being induced by the necessity of limiting the working temperature of the cooking apparatus, so as to avoid damages to the battery itself (which cannot withstand high working temperatures) and of course the trouble for its regular maintenance. For this reason, application of this technical solution has been excluded so far from the field of household cooking apparatuses.
It should finally be noticed that, in the case of household appliances with an electronic control but no clock function for the user, it would be quite useful being able to obtain information about the number and/or duration of interruptions in the operation, due to an electric supply blackout, in particular in view of the maintenance, repair and service for the apparatuses themselves.
Based on the above considerations, the present invention has the purpose to provide a method and/or an electric apparatus having an electronic control, in particular a household appliance, which is fitted with proper means which allow for estimating the duration of a more or less extended interruption of the mains voltage or blackout and, when required, solve the problem of the loss of the information relating to the current time (clock function), without the need of auxiliary energy sources, such as batteries or high rated capacitors.
These and other aims, which will be clear in the following, are reached according to the present invention by a method for estimating the duration of the interruptions in the supply from the electric mains in an electric apparatus having an electronic control, in particular a household appliance, and by an apparatus implementing such a method, having the features of the annexed claims, which form an integral part of the present description.
The present invention is based on the recognition of the fact that a solution to the problem of the loss of the current time (clock function) due to a blackout can be obtained starting from the examination of the change of the operative status of an electric apparatus, from the instant a voltage blackout occurs to the instant the voltage is restored, the law by which the status of one or more parameters monitored in the absence of electric current evolves in the time being experimentally known a priori.
To this purpose, according to the invention, the operative status of the electric apparatus can be described by the value reached by one or more quantities characterizing the operation itself. For instance, temperature is a quantity which generally characterizes very well on its own the operative status of a household appliance, whose evolution in case of an electric blackout depends on the features proper of the product (time constants of the oven, of the refrigerator, of the water heater, of the washing machine, of the dishwasher, . . . ) and on the so-called surrounding conditions (temperature inside the product and temperature of the external environment). The law according to which temperature evolves within a household appliance in case of an electric blackout can be easily derived through simple experimental tests, and be implemented equally easily in the program of a microcontroller, using proper techniques of the tabular type or based on the use of the fuzzy logic, which is well known by now.
In this way, according to the present invention, the microcontroller can be enabled to compare the value of the temperature when the electric energy is restored (power on) with the value of the temperature detected on the occasion of the blackout and; by knowing the law according to which the temperature evolves within the household appliance when no electric energy is present, to estimate with sufficient approximation the actual duration of the blackout itself, and then proceed to the clock updating.
Such an updating is performed by the microcontroller simply, by adding the estimated duration of the blackout to the value of the current time which was taken on the occasion of the blackout itself, being said value properly stored on a suitable nonvolatile memory (such as an EEPROM or a FLASH memory).
In this way a clock is obtained, which is capable of xe2x80x9cvirtuallyxe2x80x9d measuring the time also during the periods when it is unable to operate, due to a blackout of the electric mains and other backup sources (batteries or high rated capacitors).
In order to correctly perform the xe2x80x9cvirtualxe2x80x9d clock function according to the present invention, the control system of the electric apparatus should have at least the following requisites:
1. be managed by a microcontroller or other electronic device being dedicated to specific applications (ASIC);
2. have a nonvolatile memory, preferably of the EEPROM or FLASH type, capable of communicating with the microcontroller or dedicated electronic device taking charge of microcontroller""s functions, wherein informative data related to the time when a blackout has occurred are stored;
3. have suitable means which allows the microcontroller to promptly detect a blackout, so as to proceed fast (in a few tenths of milliseconds, and anyway before the microcontroller and the nonvolatile memory cease to operate properly) for storing the status of the monitored parameter and the current time;
4. finally, have in the program memory of the microcontroller all the information relating to the law of variation in the time of the quantities (or quantity) which define the status of the monitored parameter, so as to be able to estimate, on the basis of the variation of said status, the blackout duration and proceed consequently to the clock updating.
Conditions 1) and 2) are typically verified in most present electronic control systems for electric apparatuses, in particular household appliances, which usually comprise a microcontroller having proper electrically writable and erasable memory means.
With reference to condition 3), a prompt detection of a blackout and a fast storage of the current time and the system status are allowed in a simple way, by exploiting the energy accumulated in the filter capacitor of a typical microcontroller feeder, as described later.
Also condition 4), as said above, can be is easily achieved by software, following the execution of the experimental activities required for defining the law describing the evolution of a household appliance status during a blackout.
From the above, it results that the solution being proposed according to the invention does not practically involve significant additional costs for the product, though allowing it to efficiently solve the previously described problem.